on writing a while loop for rolling two dice

[Avi Gross]

For some people the "while true" method seems reasonable but it has a
problem if the internal body does not have some guarantee of an exit. And
that exit can be subtle. Many have mentioned ways an end condition can fail
due to rounding errors not being exactly equal to what you are looking for,
or an asymptotic process that approaches zero with a cutoff that is thus
never reached.

But I have seen some cases where you want a process or thread to run
indefinitely until it is killed by another process or you reboot. You could
of course use something like flag="green" and have your while keep testing
that value but that is just wasted motion. Of course, properly used, it does
help explain to the reader what your intention is, if done properly. It also
can confuse if you put in "while 5 < 6" or other weird ways to say do this
indefinitely.

I think part of this conversation is about programming styles and what we
should teach new students versus those who are trying to find more creative
ways to do things or more efficiently or more generality. Sometimes a more
direct method may be reasonable. On another forum, I saw someone write
somewhat lengthy and redundant code on how to deal with partitioning data
into three clusters randomly. My algorithm was general and handled any
number of N clusters and since N often does not cleanly divide the number of
items, has to place the remaining items into one of the N clusters or
distribute them one at a time into some to make them almost even in size.

His solution was to repeat large sections of code, three times, with some
modification, for the cases where the remainder (modulo N) was 0, 1 or 2.
The latter method was longer but in an odd way, much easier to understand.
It boiled down to, if you have one extra put it here. If you have two, put
one here and one there. My method had all kinds of bells and whistles that
this specific case did not need.

Let me end with asking if anyone has ever seen a mild variant of this:

... # code

while false
   apologize()

... # more code

-----Original Message-----
From: Python-list <python-list-bounces+avigross=verizon.net at python.org> On
Behalf Of Hope Rouselle
Sent: Thursday, September 2, 2021 10:42 AM
To: python-list at python.org
Subject: Re: on writing a while loop for rolling two dice

David Raymond <David.Raymond at tomtom.com> writes:

>> def how_many_times():
>>   x, y = 0, 1
>>   c = 0
>>   while x != y:
>>     c = c + 1
>>     x, y = roll()
>>   return c, (x, y)
>
> Since I haven't seen it used in answers yet, here's another option 
> using our new walrus operator
>
> def how_many_times():
>     roll_count = 1
>     while (rolls := roll())[0] != rolls[1]:
>         roll_count += 1
>     return (roll_count, rolls)

That's nice, although it doesn't seem more readable to a novice seeing a
while for the first time, seeing a loop for the first time, than that
while-True version.  In fact, I think the while-True is the clearest so far.
But it's always nice to spot a walrus in the wild!  (If you're somewhere
safe, that is.)
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